Backend deny

variant B1 (soft): When request wants close a task with duplicate reason and (cleaned) comment string is empty, deny closing the task and give feedback to user why it was denied.

variant B2 (hard): It requires detecting a task id in the comment field and the first detected task id is taken for referencing as ‘is duplicate of’. Limitation of this is that the duplicate could be also a ticket or something of a complete other system.